Interpolymers of ethylene and unsaturated carboxylic acids, such as acrylic acid and methacrylic acid, are well known. This present disclosure pertains to such interpolymers when made under steady state conditions in stirred reactors at high pressure and elevated temperature and using a free-radical type initiator, in contradistinction to polymers made under non-steady state conditions or in non-stirred tubular reactors or in batch reactions, and in contradistinction to block copolymers or graft copolymers.
Patents which disclose interpolymerizations of ethylene and unsaturated carboxylic acids in a steady state reaction at high temperature and high pressure in a stirred reactor in the presence of a free-radical initiator are, e.g., Canadian Pat. No. 655,298 (and its U.S. counterpart U.S. Pat. No. 4,351,931): U.S. Pat. Nos. 3,239,370; 3,520,861; 3,658,741; 3,884,857; 3,988,509; 4,248,990; and U.S. Pat. No. 4,252,924.
U.S. Pat. No. 3,239,370 discloses a random copolymerization of ethylene with an unsaturated carboxylic acid (e.g. acrylic acid) in a stirred autoclave operated at 16,000 psi, and 210.degree. C. using a peroxy initiator, the so-formed copolymer being particularly useful as a coating for non-metallic substrates.
U.S. Pat. No. 3,520,861 discloses a substantially homogeneous, compositionally uniform, random copolymer of ethylene/unsaturated acid (e.g. acrylic acid, methacrylic acid, crotonic acid) prepared in a continuous manner in a stirred autoclave at high pressure and elevated temperature, using a free-radical initiator (such as a peroxide). The temperature of the polymerization is disclosed as being in the range of about 120.degree. C. to about 300.degree. C., preferably about 150.degree. C. to about 250.degree. C. The pressure of the polymerization is disclosed as being in the range of at least 1000 atmospheres, preferably between about 1000-3000 atmospheres, esp. between 1100-1900 atmospheres.
Canadian Pat. No. 655,298 and its U.S. counterpart (U.S. Pat. No. 4,351,931) discloses homogeneous, compositionally uniform, random copolymers of ethylene and unsaturated carboxylic acids (e.g. acrylic acid) wherein said copolymer comprises at east about 90% by weight of ethylene with a melt index of 0.01 to 30 g/10 minutes. The copolymers are prepared in a well-stirred reactor at a pressure of at least 1000 atmospheres, at 90.degree.-280.degree. C., using a free radical initiator, while maintaining the ratio of monomers (ethylene/acid) in the range of 10,000/1 to 50/1 by weight, the process being performed continuously by feeding monomers in, while removing reaction mixture, and maintaining a constant reaction environment.
U.S. Pat. No. 3,658,741 discloses homogeneous copolymers of ethylene and unsaturated carboxylic acids and esters, prepared in the presence of a chain transfer agent, a free radical catalyst, a temperature between 100.degree. C.-300.degree. C. and pressure between 100 and 1000 atmospheres, using turbulent agitation; the reaction is said to take place in the vapor phase and prepares very low mol. wt. copolymers.
U.S. Pat. Nos. 3,884,857 and 3,988,509 disclose the preparation of copolymers, such as ethylene/acrylic acid copolymers in a continuous, high pressure, freeradical polymerization process, at 100.degree.-250.degree. C. and 1000-2500 atmospheres of pressure.
U.S. Pat. No. 4,248,990 discloses copolymers, e.g. ethylene/acrylic acid copolymers which are said to distinguish over the random copolymers of Canadian Pat. No. 655,298 and of U.S. Pat. No. 3,520,861 by virtue of being non-random. This non-randomness is said to be the result of operating the steady state, high pressure, stirred reactor at a pressure of from 0 to about 500 psi above, and at temperature of from 0.degree.-15.degree. C. above, that needed to maintain a single phase reaction mixture at the given concentration of copolymer in the reaction mixture and at the given acid comonomer content of the copolymer.
U.S. Pat. No. 4,252,924 discloses the preparation of non-random copolymers, e.g. ethylene/acrylic acid copolymers in at least two constant environment, stirred autoclaves in series, each using a single phase reaction mixture, but where each succeeding autoclave is maintained at a temperature of at least 30.degree. C. above that of the preceding autoclave.
In the ordinary course of events, operators of processes are not inclined to empoy more energy (temperature and/or pressure) than is deemed necessary to obtain a given product, in the absence of any recognized benefit to be derived from such additional expense. We have now found that there are unexpected benefits to be derived from employing more energy (temperature and pressure) than is generally deemed to be sufficient in the production of interpolymers of ethylene.